This application relates to a ladder system used between a pair of laterally spaced apart storage shelves located in a store or warehouse. Applicant's prior U.S. Pat. No. 5,413,191, issued May 9, 1995, entitled “DUAL TRACK LADDER” and U.S. Pat. No. 6,619,427, issued Sep. 16, 2003, entitled “FOLDABLE DUAL TRACK LADDER” disclose ladder systems which have been commercially successful. The existing dual track ladders have spring-loaded casters and rubber pads at the lower end of the ladder. When the ladder is in use, the weight of the user or worker is sufficient to compress the caster springs and urge the rubber pads against the floor to thereby lock, secure or immobilize the base of the ladder on the floor.
However, with taller ladders and especially ladders provided with a platform for the user or worker at the top of the ladder, some have found that the construction of the ladder permitted movement of the upper part of the ladder longitudinally parallel to the dual tracks despite the compression of the spring casters at the base of the ladder as in U.S. Pat. No. 6,619,427. Also, it was found that the ladder was slightly unstable on the transverse track or rod forming a part of the roller carriage and thus the top of the ladder could also move slightly laterally or from side to side. Such movements are undesirable.
With the prior art ladders, a person can inch the ladder forward or longitudinally as well as laterally despite the compressed spring-loaded casters at the base. The wheels or rollers on the dual tracks and on the wheels or rollers on the lateral track at the top of the ladder have no restraint and by jerking the ladder forward, a person can move the ladder either intentionally or mistakenly forward as well as laterally from side to side.